Freeze indicator employing light scattering and method of making same

ABSTRACT

A freeze indicator including an indicator dispersion is described herein. Such an indicator dispersion can include: a liquid medium and particles of a colored indicator agent dispersed in the liquid medium. The colored indicator agent particles having an inherent color; wherein the indicator dispersion exhibits the inherent color of the colored indicator agent particles after freezing and is configured to have a less colored appearance before freezing and wherein light scattering masks the inherent color of the colored indicator agent particles before freezing. Some indicator dispersions can be free of color-changing chemical co-reactants. These freeze indicators can be small, have a low cost, and have a simple configuration.

PRIORITY CLAIM AND CROSS-REFERENCE TO A RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/968,895, filed on Aug. 16, 2013, which claims the benefit ofprovisional patent Application No. 61/683,805, filed on Aug. 16, 2012,the entire disclosures of these applications are incorporated byreference herein for all purposes.

The present disclosure relates, inter alia, to a freeze indicator formonitoring past exposure of a host product to a freezing temperature,and to a method of manufacturing such a freeze indicator.

BACKGROUND

Many commercial products are freeze-sensitive and may lose efficacy orquality if they experience freezing temperatures before use. Examples offreeze-sensitive commercial products include certain pharmaceuticals,medical products, and foodstuffs as well as some industrial products.Accordingly, various freeze indicators have been provided that canmonitor freeze exposure and signal when a freezing, or near-freezingevent has occurred. The signal can be a color change, for example, achange in the color of an indicator area, and can be generated by anindicator dispersion that coagulates upon freezing to provide the colorchange. Some examples of known freeze indicators are described in U.S.Pat. No. 8,128,872 to Lentz et al., U.S. Pat. No. 8,122,844 to Smith etal., U.S. Pat. Nos. 7,891,310; 7,624,698; 7,571,695; 7,490,575 and7,343,872 to Taylor et al. and U.S. Patent Application Publication No.2012/0079980 by Taylor et al. (Taylor '980 herein). The disclosure ofTaylor '980 is incorporated by reference herein.

While known freeze indicators may be satisfactory for their intendedpurposes, nevertheless, a need exists for a freeze indicator having newcharacteristics.

BRIEF SUMMARY

It would be desirable to provide a freeze indicator, of the typeemploying an indicator dispersion including an aqueous liquid medium,that can provide a distinct color change in small, low cost embodiments,in which the indicator dispersion has a simple configuration.

Some embodiments include an indicator dispersion comprising: a liquidmedium; and particles of a colored indicator agent dispersed in theliquid medium, the colored indicator agent particles having an inherentcolor; wherein the indicator dispersion exhibits the inherent color ofthe colored indicator agent particles after freezing and is configuredto have a less colored appearance before freezing and wherein lightscattering masks the inherent color of the colored indicator agentparticles before freezing; and wherein the indicator dispersion is freeof color-changing chemical co-reactants.

Some embodiments include an indicator dispersion comprising: a liquidmedium; and liquid particles of a colored indicator agent dispersed inthe liquid medium, the colored indicator agent particles having aninherent color; wherein the indicator dispersion exhibits the inherentcolor of the colored indicator agent particles after freezing and isconfigured to have a less colored appearance before freezing and whereinlight scattering masks the inherent color of the colored indicator agentparticles before freezing.

With respect to an indicator dispersion above, in some embodiments, theindicator dispersion is free of color-changing chemical co-reactants. Insome embodiments, the liquid medium is a hydrophobic liquid medium. Insome embodiments, the liquid medium is an aqueous liquid medium.

Some embodiments include a freeze indicator having a housing and theindicator dispersion disposed within the housing. The housing can beconfigured for the indicator dispersion to be optically readableexternally of the freeze indicator.

Some embodiments include a freeze indicator having a housing and anindicator dispersion disposed within the housing. The housing can beconfigured for the indicator dispersion to be optically readableexternally of the freeze indicator. The indicator dispersion can includean aqueous liquid medium and particles of a colored indicator agentdispersed in the aqueous liquid medium. The colored indicator agentparticles can have an inherent color and the indicator dispersion canexhibit the inherent color of the colored indicator agent particlesafter freezing. Also, the indicator dispersion can be configured to havea less colored appearance before freezing wherein light scattering masksthe inherent color of the colored indicator agent particles beforefreezing. The light scattering can be random scattering of incidentlight. Further, in some cases, the light scattering can give theindicator dispersion a whitish appearance. Further, the indicatordispersion can coagulate in response to exposure to a freezingtemperature.

In some embodiments of the freeze indicator the colored indicator agentparticles include a colorant dissolved in a hydrophobic liquid, forexample, an oil. In another embodiment of the freeze indicator thecolored indicator agent particles include solid particles of colorantdispersed in a hydrophobic liquid, for example, an oil. In otherembodiments, the colored indicator agent particles can include solidparticles of a colorant dissolved or dispersed in a solid material.

Some embodiments include a freeze indicator including a housing and anindicator dispersion within the housing. The housing can be configuredfor the indicator dispersion to be optically readable externally of thefreeze indicator. The indicator dispersion includes an aqueous liquidmedium and liquid particles of a colored indicator agent dispersed inthe aqueous liquid medium. The colored indicator agent particles caninclude a colorant dissolved in a hydrophobic liquid and can have aninherent color. The indicator dispersion can exhibit the inherent colorof the colored indicator agent particles after freezing and can beconfigured to have a less colored appearance before freezing. Lightscattering, or another suitable phenomenon can mask or conceal theinherent color of the colored indicator agent particles before freezing.

In one embodiment of freeze indicator, the colorant is a dye and thehydrophobic liquid is an oil. The colored indicator agent particles canbe homogenous, for example, all or essentially all the particles canhave essentially the same composition as each other. Also, there can beno other indicator particles present in the indicator dispersion orthere can be an absence from the indicator dispersion of other indicatorparticles that could participate in a change in appearance of the freezeindicator in response to freezing. Further, the indicator dispersion canbe free of color-changing chemical co-reactants, if desired.

Some embodiments include a method of making a freeze indicator includingdispersing particles of a colored indicator agent in an aqueous liquidmedium to provide an indicator dispersion and configuring the indicatordispersion to have less color before freezing. The method can alsoinclude loading the indicator dispersion into a housing that permits theindicator dispersion to be optically readable externally of the freezeindicator. The colored indicator agent particles can imbue the indicatordispersion with a appearance after freezing.

In some freeze indicator embodiments, the colored indicator agentparticles can have an average particle size of at least about 100 nm orat least about 200 nm. Alternatively, or in addition, to any of theforegoing minimum proportions, the colored indicator agent particles canhave an average particle size not more than about 2 μm, or of not morethan about 1.2 μm. Optionally the average particle size can be in arange of from about 200 nm to about 500 nm. The method can includeconfiguring the indicator dispersion to have any average particle sizecorresponding with one or more of these criteria.

In this method, the indicator dispersion can exclude or be free ofcolor-changing chemical co-reactants. Also, the indicator dispersion cancoagulate in response to exposure of the indicator dispersion to afreezing temperature.

Embodiments of freeze indicators can provide a distinct color change insmall, low cost units suitable for monitoring host products for possiblefreeze exposure. A variety of different colored indicator agentparticles, which can employ various colorants, can be employed,providing a range of options for practicing the invention. The indicatordispersion can have a simple configuration and the invention includessimple methods of making freeze indicators.

Some embodiments include a label for a perishable good, comprising afreeze indicator described herein.

Some embodiments include a package for a perishable good, comprising afreeze indicator described herein.

Some embodiments include a package containing a perishable good,comprising a freeze indicator described herein.

Some embodiments include a method of protecting a perishable item,comprising coupling the perishable item with a freeze indicatordescribed herein so that the freeze indicator is subject tosubstantially the same temperature conditions as the perishable item.Such a method may further comprising inspecting the freeze indicator forthe detectable and irreversible change in the apparent color of theindicator dispersion. If desired, the item could be discarded if thedetectable and irreversible change in the apparent color of theindicator dispersion is detected.

Some embodiments include use of a freeze indicator described herein inmonitoring the quality of a perishable good.

Some embodiments include a method of detecting a freezing event,comprising subjecting a freeze indicator of described herein toconditions under which a freezing event might occur, and observingwhether a detectible and irreversible change in the apparent color ofthe indicator dispersion occurs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Some embodiments, and ways of making and of using one or moreembodiments, are described in detail herein and, by way of example, withreference to the accompanying drawings (which are not necessarily drawnto scale with regard to any internal or external structures shown), inwhich like reference characters designate like elements throughout theseveral views, and in which:

FIG. 1 is a plan view of a freeze indicator employing light scatteringaccording to one embodiment;

FIG. 2 is a sectional view on the line 2-2 of the freeze indicator shownin FIG. 1;

FIG. 3 is a view similar to FIG. 2 of a freeze indicator employing lightscattering according to another embodiment; and

FIG. 4 is a view of a number of samples of freeze indicator dispersionsshowing their before-freezing appearances and their after-freezingappearances.

DETAILED DESCRIPTION

Administration of vaccines provides a cost-effective health interventionthat can save or improve, millions of lives globally. The biologicalactivity of vaccines is attributable to complex organic macromolecules,for example, proteins, having particular three-dimensionalconformations. When exposed to freezing temperatures, or in some cases,to near-freezing temperatures, vaccines can lose potency because the lowtemperature destroys the particular conformation of one or moreessential organic macromolecules in the vaccine composition. Alow-potency vaccine, if administered to a subject, may fail to protectthe subject from a serious or fatal disease.

Because warm temperatures also can affect vaccine quality adversely,vaccines are generally refrigerated, or cooled by other means, duringstorage and distribution to end users. Such cooling means introduce arisk that some or all vaccine samples in a batch of samples may sufferexposure to freezing or near-freezing temperatures due to cold spotswithin a container, poorly controlled refrigeration, or other factors.Similar considerations apply to various other commercial products, forexample, biological pharmaceuticals and some genetically engineeredpharmaceuticals, as well as certain foodstuffs, and other commercialproducts, some of which are described elsewhere herein.

To help mitigate this problem, a freeze indicator can be associated witha vaccine, or another host product, to provide an optical signalalerting a health worker, or other end user, that the vaccine may havelost potency and possibly should not be used.

Taylor '980 describes various freeze indicators that can be embodied insmall, low cost, label-like configurations suitable for mass-productionand adhered to, or otherwise associated in close proximity, with hostproducts such as vaccine vials or syringes.

Taylor '980 describes, inter alia, a freeze indicator that includes acolor-changing emulsion employing first and second reactant phasesdispersed in a dispersion medium that can be an aqueous liquid. Thefirst and second reactant phases can include a first reactant and asecond reactant that can co-react in response to exposure to a freezingtemperature, changing the color of the color-changing emulsionirreversibly. As described, various co-reactants can be employed, someof which can provide an intense color change and good contrast betweenthe after-freezing appearance and the initial appearance of the freezeindicator.

For some purposes, it would be desirable to provide a low-cost freezeindicator suitable for use with vaccines and other host products thatincludes an indicator dispersion having a simple composition and havingan after-freezing appearance that contrasts well with thebefore-freezing appearance of the indicator dispersion. Othercharacteristics that would be useful, in some cases, include having anindicator dispersion that is easy to manufacture, and an ability to beconfigured as a label, optionally, as a thin flexible label.

To address such needs, some embodiments include a freeze indicatoremploying an indicator dispersion that includes an aqueous liquidmedium, or a hydrophobic liquid medium, in which particles of a coloredindicator agent are dispersed and in which the indicator dispersion canbe configured to have a less colored appearance before freezing and amore colored appearance after freezing. The colored indicator agentparticles can have an inherent color that provides the more coloredafter-freezing appearance, and, for simplicity, the indicator dispersioncan exclude, or be free of, color-changing chemical co-reactants. Suchan indicator can provide the benefits of simplicity, ease ofmanufacture, and/or a good color contrast between the after-freezingappearance and the before-freezing appearance.

For example, some embodiments of freeze indicators can include anindicator dispersion that has a single phase of colored indicator agentparticles dispersed in the aqueous (or hydrophobic) liquid medium, thesingle phase of colored indicator agent particles being the onlydispersed phase in the indicator dispersion. The particles in the singlephase of colored indicator particles can be homogenous, with essentiallysimilar compositions to each other. Such embodiments of freeze indicatorare unlike freeze indicators that employ two different reactive phasesdispersed in an aqueous liquid medium. Some embodiments include a freezeindicator wherein the colored indicator agent particles consist of asingle colorant dissolved or dispersed in a single hydrophobic liquid ora single solid dispersed in an aqueous liquid medium. Such indicatordispersions can include an ice nucleant, a dispersion stabilizer, aprotein stabilizer, a low-temperature destabilizer and/or a biocide asan optional ingredient or ingredients.

Some examples of materials that can be excluded from the indicatordispersion to assure that the indicator dispersion include nocolor-changing chemical co-reactants are: a chemical reactant that canco-react with the colored indicator agent particles and chemicallymodify the color of the particles, for example, a color-depleting agent;a color precursor accompanied by a color developer; and a color-changingchemical reactant that can react with another component of the freezeindicator to provide color. Avoidance of such materials can simplify theconfiguration of the indicator dispersion and can reduce issues that maysometimes arise, for example, undesired background color in thebefore-freezing appearance of the indicator dispersion.

In a multi-phase system that includes color-changing chemical reactants,for example, an oil-in-water dispersion or a water-in-oil dispersion,chemical reactants included in the oil phase may migrate into theaqueous phase. Migration of color-changing chemical reactants into,and/or through, the aqueous phase can lead to a premature color changingreaction that may confuse the indicator signal, in some cases, forexample, by darkening the initial color of the indicator dispersion andreducing the contrast between the before and after appearances of theindicator.

Indicator dispersions employed in freeze indicator embodiments can beconfigured to utilize light scattering to mask or conceal the inherentcolor of the colored indicator agent particles by adjusting the averageparticle size of the hydrophobic material to have values conducive tolight scattering. The particle size can be configured to cause theindicator dispersion to have an appearance that is different from theinherent color of the colored indicator agent particles as a result of aphenomenon other than light scattering if such other phenomenon providesa distinct contrast between the before-freezing appearance of theindicator dispersion and the after-freezing appearance of the indicatordispersion. In the case of an emulsion, increasing the intensity and/orthe duration of homogenization during manufacture usually will decreasethe particle size of the indicator dispersion. Higher agitation speedsand/or more sophisticated equipment usually can be employed to increasethe intensity of homogenization, as will be known to a person ofordinary skill in the art. Suitable dispersions can be fabricated bycomparable methods.

Use of a hydrophobic material having a relatively high refractive index,for example, greater than about 1.45 or 1.5, can help provide a lesscolored, a more opaque, or lighter colored dispersion, in some cases.Some examples of hydrophobic materials having useful refractive indexesare vegetable oils such as olive oil and sunflower oil, which haverefractive indices of about 1.47, and mineral oil, which has arefractive index of about 1.48. Hydrogenated terphenyl oils, which havehigher refractive indices of about 1.52, may provide more opacity orlightness and can be employed also.

The intensity of the color of the dispersed phase (colorant in oil orwater itself) can be varied to affect the distinction between theindicator states before and after freezing. Color intensity of liquidscan be measured with densitometry, spectrometry or by comparison tovisual standards. The color intensity obtained by a 1 cm thick liquid isits absorbance. When absorbance is to be measured by spectroscopy awavelength can be selected that corresponds to the color. For example ifthe colorant is red the color absorbance can be measured at 700 nm; ifblue, the color absorbance can be measured at 475 nm. Black or gray maybe measured at any wavelength in the visible spectrum, but it may beconvenient to measure at 500 nm. The actual color intensity of acolorant solution or dispersion is dependent upon both the concentrationof the colorant and the relative strength of the colorant. Useful rangesfor the absorbance of black liquids are 1 to 30, 2 to 20, or 3 to 10. Insome embodiments, a colored indicator agent, such as a hydrophobic oilcontaining a colorant, has an absorbance at 500 nm of about 1 to about30, about 2 to about 15, or about 3 to about 10.

The concentration of colorant can be varied for different colorants,having different color intensities, that may be utilized in the coloredindicator agent particles, to provide a strong post-freezing color and adistinct color change. Alternatively, or in addition, to any of theforegoing minimum proportions, the proportion of colorant can be notmore than about 1.0 percent, not more than about 0.1 percent or not morethan about 0.05 percent by weight. Optionally, the proportion can befrom about 0.001 percent to about 0.01 percent. The proportion ofcolorant can be decreased to reduce color in the before-freezingappearance, if present, or can be increased to increase color in theafter-freezing appearance, if desired. Any such proportion of colorantcan be employed in a method embodiment.

Indicator dispersions employed in freeze indicator embodiments of theinvention can have various proportions of colored indicator agentparticles, for example, a proportion by weight based upon the weight ofthe indicator dispersion of at least about 0.0005 percent, or at leastabout 0.002 percent, at least about 0.01 percent, at least about 0.05percent. Alternatively, or in addition, to any of the foregoing minimumproportions, the proportion of colorant can be not more than about 1.0percent, not more than about 0.1 percent or not more than about 0.05percent by weight. Optionally, the proportion can be from about 0.001percent to about 0.01 percent.

The proportion of colorant can be decreased to reduce color in thebefore-freezing appearance, if present, or can be increased to increasecolor in the after-freezing appearance, if desired. Any such proportionof colorant can be employed in a method embodiment of the invention.Indicator dispersions employed in freeze indicator embodiments can havevarious proportions of colored indicator agent particles, for example, aproportion by weight based upon the weight of the indicator dispersionof at least about 50 percent, or at least about 30 percent, at leastabout 20 percent, at least about 5 percent.

Further, indicator dispersions employed in some freeze indicatorsembodiments can consist only of an aqueous liquid medium and coloredindicator agent particles, or can include one or more optionaladditional ingredients such as a dispersion stabilizer and an icenucleant. A suitable dispersion stabilizer or stabilizers, if employed,can stabilize the indicator dispersion at above-freezing temperaturesand permit the indicator dispersion to collapse at or below freezingtemperatures. A suitable ice nucleant can help control supercooling andraise the temperature at which the indicator dispersion begins to freezeto be closer to the melting point of the aqueous liquid medium. Someadditional ingredients that can be included are a low-temperaturedestabilizer, a protein stabilizer, and a biocide, as describedelsewhere herein.

The terms “coagulate” and the grammatical variations thereof, including“coagulating” and “coagulation”, are used in this specification to referto gathering together, or forming into a mass or a group, where the partall remain distinct.

The terms “coalesce” and the grammatical variations thereof, including“coalescing” and “coalescence” are used in this specification to referto growing together, uniting or joining together, into one body,product, mass, or becoming integrated into a whole. In the cases of theemulsions described herein, coalescence can be understood generally, butnot always, to be preceded by coagulation. It will be understood that afreeze indicator dispersion that coalesces can coalesce into more thanone body or masses of coalesced particles.

The term “color” is used herein to refer to achromatic visualappearances, for example, black, gray, and white, and chromatic visualappearances, including primary color hues, secondary color hues and/orother color hues, for example, without limitation, red, yellow, green,blue, purple, orange, and brown. The terms “color change” and itsgrammatical variants, or equivalents, are used to refer to changes inhue, intensity or lightness (or darkness) or other changes in visualappearance. A “light” appearance or a “dark” appearance refers to thegrayscale appearance without reference to any hue that may, or may not,be present. A “more colored” appearance refers to a color that is morereadily discernable as compared to an appearance that either colorlessor white. For example, a light yellow or a pink color is more coloredthan white.

The terms “particle” and “particles” used herein in regard to adispersion includes both solid particles and liquid particles.

The term “dispersion” is used herein to refer to a dispersion of solidparticles in a liquid medium, or a dispersion of liquid particles, in aliquid medium. The term “emulsion” is used herein to refer to adispersion of liquid particles in a liquid medium, for example, anoil-in-water emulsion or a water-in-oil emulsion.

Some examples of color changes that can be exhibited by some freezeindicators include changes between any two of white, gray, black, red,yellow, blue, green, purple, orange and brown, and any tints and shadesof the foregoing colors. Some embodiments of freeze indicator canexhibit a change from white, light or colorless before freezing toyellow, orange, green, red, black or violet after freezing.

The term “freezing temperature” is used herein to refer to a temperaturethat will cause an aqueous freeze indicator dispersion medium, such asis described herein, to form ice crystals.

The term “freeze” and grammatical variations thereof, including“freezing,” is used to refer to the freezing of water.

The term “optical density” (OD) as used herein refers to the log to thebase 10 of the inverse of the incident light reflected from a sample. ODcan be expressed by the formulaOD _(λ)=log₁₀(I ₀ /I)where I is the intensity of light at a specified wavelength λ that isreflected by a sample and I₀ is the intensity of the light before itenters the sample.

The term “water” is used herein to include deuterium oxide anddeuterated water as well as ordinary “light” water.

In some embodiments, suitable indicator dispersions can be formulated asa simple oil-in-water emulsion or a water-in-oil emulsion. Someembodiments can employ a simple dispersion of hydrophobic particles inwater. Before freezing, notwithstanding that a colorant is present, suchan indicator dispersion can scatter light, appearing light, lesscolored, or white in color. The appearance of the indicator dispersioncan also be opaque, in some cases. Light scattering can mask or concealthe inherent color of the colored indicator agent particles that arepresent in the indicator dispersion. The light scattering can be randomscattering of incident light.

Upon exposure of the freeze indicator to a freezing temperature,freezing of water can cause coalescence of oil particles in theemulsion. In response to freezing, the emulsion can sometimes break intotwo phases that are largely or entirely coalesced into two distinctvolumes, one of which volumes displays the color of the coloredindicator agent particles. In other cases, the oil particles cancoalesce on thawing of the aqueous phase into multiple larger particles,bodies or masses that exhibit the inherent color of the colorant, forexample by reflection of incident light. Similarly, in response tofreezing, a solid particle dispersion can break, causing coagulation ofthe solid particles in the indicator dispersion into masses that nolonger scatter light strongly, but display the inherent color of thecolored indicator agent particles in the indicator dispersion. Thecolored indicator agent particles can become irreversibly coagulatedafter freezing.

A surprisingly intense color change can be obtained in some freezeindicator embodiments that employ relatively simple indicatordispersions, as described herein, by utilizing a suitable concentrationof an appropriate colorant. For example, the after-freezing appearanceof a layer of the indicator dispersion having a thickness of 1 mm can beat least 0.4 optical density (“OD”) units darker than thebefore-freezing appearance of the layer of the indicator dispersion.

Effective masking of intense color by light scattering in freezeindicator embodiments using relatively simple indicator dispersions, asdescribed herein, also is unexpected. Further, some embodiments offreeze indicator surprisingly can employ an intense colorant, forexample, an opaque black dye, yet have a before-freezing appearance thatis white and largely or completely free of background color, cast, ortinge. Using an opaque black dye, the before-freezing appearance in suchembodiments does not appear to be gray.

Freeze indicators embodiments can be formulated with a variety of coloroptions, as a variety of different colorants can be used, including, forexample, various oil-soluble dyes and various water-insoluble pigments.Moreover, the simplicity of the indicator dispersions that can beemployed makes a range of options available for the configuration of theindicator dispersion and for the materials employed. For example, adiversity of colored indicator agents can be employed, and otheringredients, such as hydrophobic liquids, solid materials, dispersionstabilizers, and ice nucleants, if present, can be selected from a rangeof acceptable candidates.

While simplicity may have benefits, the invention is not limited tosimple embodiments.

Colored indicator agent particles employed in freeze indicatorembodiments can have various particle sizes, for example, an averageparticle size of at least about 100 nm or at least about 200 nm. Theaverage particle size can be not more than about 1.2 μm, or not morethan about 2 μm. Optionally, the average particle size can be from about100 nm to about 400 nm.

Freeze indicator embodiments can be configured to be associated with ahost product to monitor the host product for exposure to a freezingtemperature. For this purpose, the freeze indicator can include asubstrate supporting the housing and the substrate can be adapted to beaffixed to the host product or to a package or other container for thehost product. For example, the substrate can have a coating of apressure-sensitive adhesive to secure the freeze indicator to the hostproduct or the container. The pressure-sensitive adhesive can beprotected with a release liner prior to application of the freezeindicator to a host product, or to a container for the host product.Alternatively, the freeze indicator can be affixed to the host productby a tie or other means, or can be inserted in the container for thehost product, if a container is employed.

The substrate, if a substrate is employed, or another element of thefreeze indicator can bear a reference area colored, for example, byprinting, to show the after-freezing appearance of the indicator, ifdesired. Further, the substrate can bear printed indicia providinginstructions for use, indications of origin, host-product information,marketing information, and/or other desired material.

Optionally the housing and substrate, if employed, can be flexible tofacilitate attachment of the freeze indicator to a curved surface of ahost product and to enable the freeze indicator to conform with thecurved surface.

Freeze indicator embodiments can be mass produced using packagingmachinery and packaging methods, or the like. In one method ofmanufacture, freeze indicators can be assembled into individuallydie-cut items mounted with pressure sensitive adhesive on continuouslengths of release liner in sheet or roll form. The sheets or rolls offreeze indicator can be manipulated like labels and can be applied tohost products or their containers using appropriately modifiedmechanical label applicators.

As noted previously herein, in some embodiments, the colored indicatoragent particles can include a colorant dissolved or dispersed in ahydrophobic liquid, or in a solid material.

Colorant.

For hydrophobic colored indicator agent particles, the colorant can be,or can include one or more oil-soluble dyes or oil-dispersible pigments.A dye or dyes having a low water-solubility can be employed. Good oilsolubility of the dye can enhance the color intensity of thepost-freezing appearance of the indicator dispersion. Low watersolubility can avoid or reduce possible migration of the dye or pigmentinto the aqueous liquid medium, which may cause premature coloration ofthe indicator dispersion. For example, the dye can have a watersolubility of not more than about 10 mg/mL, not more than about 1 mg/mL,or not more than about 0.1 mg/mL. Suitable oil-solubilities for usefuldyes can vary and can be, for example, at least about 10 mg/mL, at leastabout 50 mg/mL or at least about 100 mg/mL. Usefully, the dye can havesubstantially greater solubility in oil than in water. For example, thedye can be at least two times, at least five times, at least ten times,at least fifty times or at least one hundred times more soluble in oilthan in water, the solubilities being solubilities by weight.

For aqueous colored indicator agent particles, the colorant can be, orcan include one or more water-soluble dyes or water-dispersiblepigments. A dye or dyes having a low oil-solubility can be employed.Good water solubility of the dye can enhance the color intensity of thepost-freezing appearance of the indicator dispersion. Low oil solubilitycan avoid or reduce possible migration of the dye or pigment into thehydrophobic liquid medium, which may cause premature coloration of theindicator dispersion. For example, the dye can have an oil solubility ofnot more than about 10 mg/mL, not more than about 1 mg/mL, or not morethan about 0.1 mg/mL. Suitable water-solubilities for useful dyes canvary and can be, for example, at least about 10 mg/mL, at least about 50mg/mL or at least about 100 mg/mL. Usefully, the dye can havesubstantially greater solubility in water than in oil. For example, thedye can be at least two times, at least five times, at least ten times,at least fifty times or at least one hundred times more soluble in waterthan in oil, the solubilities being solubilities by weight.

Various colors can be employed for the colorant. Red, orange, and blackare examples of colors that can help signal that an adverse conditionmay have arisen, and are advantageous as they follow common conventionsfor indicating unsatisfactory or dangerous conditions, or as a warning.Some examples of suitable dyes include: solvent dyes; Solvent Blue 35,an anthraquinone solvent dye that has a low water-solubility of about 6mg/mL; Solvent Green 3 an aminoanthraquinone solvent dye that is onlysparingly soluble in water, having a water-solubility of about 0.9mg/mL; Solvent Black 3, also called Sudan Black B, a disazo solvent dyehaving two functional azo (—N═N—) groups that also is only sparinglysoluble in water, with a water-solubility of about 0.1 mg/mL; Oil Red O;and Victoria Blue B both available from Sigma-Aldrich, (St. Louis, Mo.);and KEYPLAST (trademark) Liquid Oil Red HF, KEYPLAST Black 2B andKEYPLAST Black AN available from Keystone Aniline Corporation.Additional information regarding further useful oil-soluble dyes, commonnames, chemical structures and water solubilities of useful dyes can befound, for example, in Floyd J. Green “Handbook of Stains, Dyes, andIndicators,” The Aldrich Chemical Company (1991).

Some examples of suitable pigments include carbon black, iron oxide orultramarine. A pigment employed can be treated to enhance thedispersibility of the pigment in a hydrophobic material, if desired, forexample, by coating the pigment particles with a hydrophobic coating. Apigment employed can be treated to enhance the dispersibility of thepigment in an aqueous medium, if desired, for example, by coating thepigment particles with a hydrophilic coating.

Other suitable colorant colors, dyes, and pigments will be apparent to aperson of ordinary skill in the art, or will become apparent as the artdevelops.

Hydrophobic Liquid.

Hydrophobic liquids that can be employed can be liquids that aredispersible in the aqueous liquid medium, or in which water can bedispersed, without undue difficulty, as components of the coloredindicator agent particles. Desirably, the hydrophobic liquid can becapable of adopting a particle size that can mask the inherent color ofthe colored indicator agent particles, or that can otherwise produce asuitable difference in appearance after freezing. Some suitablehydrophobic liquids are liquid at freezing temperatures (and thereforealso at higher temperatures), for example, at temperatures down to 0°C., −5° C., or −10° C. However, a hydrophobic liquid that is liquid atordinary ambient temperatures but which is frozen at or near 0° C. canalso be used, if solid particles of the frozen hydrophobic liquid can becoagulated into visible agglomerates or masses. Such aggregates maycoalesce on melting of the frozen hydrophobic liquid and increase thedifference in appearance following freezing and thawing.

Some examples of suitable hydrophobic liquids include, inter alia,natural oils and synthetic oils. Some useful hydrophobic liquids arewater-immiscible or tend to repel, or not absorb, water, and/or have alack of affinity for water. A useful hydrophobic liquid can be ahydrophobic liquid that is unreactive with other components of theindicator dispersion, or with any housing or containment material thatthe freeze indicator may employ to contain the indicator dispersion andthat contacts the indicator dispersion. More particularly, but notexclusively, the hydrophobic liquid can be unreactive with the colorant.Examples of suitable hydrophobic liquids include mineral oil, terphenyloils, vegetable oils, soy bean oil, cottonseed oil, linseed oil, rapeseed oil, castor oil, sunflower oil, olive oil, canola oil, peanut oil,corn oil, and silicone oils or silicone fluids, for example, siloxanes,polysiloxanes cyclopolysiloxanes, and dimethicone. One suitablepartially hydrogenated terphenyl oil is available under the product codeMCS 2811 from Solutia, St. Louis, Mo. A mixture of two or morehydrophobic liquids also can be used. Some further suitable hydrophobicliquids are described in Taylor '980.

One advantage of using a water-in-oil emulsion as an indicatordispersion is that the freezing point of an oil medium is more flexiblethan that of an aqueous medium because oils have a much greater range ofmelting points than aqueous solutions. In some embodiments, the aqueousmedium is a hydrophobic liquid having a melting point of about 0° C. toabout 100° C., about 2° C. to about 20° C., about 5° C. to about 20° C.,about 5° C. to about 10° C., about 10° C. to about 15° C., or about 15°C. to about 20° C.

Solid Material.

In other embodiments, the colored indicator agent particles can includea colorant dissolved or dispersed in a solid material. Examples ofsuitable solid materials, which, optionally, can be soft, as describedherein, include various hydrophobic materials, various wax materials,such as, paraffin wax, microcrystalline wax, carnauba wax, beeswax,Chinese wax, shellac wax, spermaceti, tallow, palm wax, soy wax, andlanolin and mixtures of two or more wax materials. Further examples ofsuitable solid materials include various synthetic polymers andcopolymers, such as, polyethylene, polypropylene, polyvinylidene, andpolyvinylchloride and mixtures of two or more polymers and orcopolymers. In further embodiments, the colored indicator agentparticles can be solid particles of a colorant dispersed in ahydrophobic liquid or in a solid material. The colorant can be apigment, or a water-insoluble dye, that normally exists in the solidstate at temperatures at which a freeze indicator may be used, forexample, up to about 50° C.

Aqueous Liquid Medium.

The aqueous liquid medium can include, or consist of, any suitableaqueous liquid for example, water. Optionally, one or morewater-miscible liquids having a melting point higher than that of watercan be included in the aqueous liquid medium, for example deuteriumoxide, deuterated water or a mixture of deuterium oxide and deuteratedwater. In some embodiments of freeze indicator, the aqueous liquidmedium can include at least about 90 percent by weight, based on theweight of the aqueous liquid medium, of deuterium oxide, for example,100 percent, or another suitable proportion. The aqueous liquid mediumcan be configured to have a melting point related to a temperaturecondition to be monitored by suitable selection of aqueous ingredientsand their proportions. The aqueous liquid medium can be colorless, andcan be free of added colorants, other than the colored indicator agentparticles, if desired. Alternatively, a desired colorant can be includedin the aqueous liquid medium, by dissolution, or in another suitablemanner. Some suitable aqueous liquid media are also described in Taylor'980, for example, in paragraphs 0188-0198.

Ice Nucleant.

Indicator dispersions employed in freeze indicator embodiments also caninclude an ice nucleant to help overcome supercooling and provide afreeze response at a temperature closer to the melting point of thedispersion medium than would occur if the ice nucleant were not present.An ice nucleant can reduce the effect of supercooling, elevate thefreezing temperature of the aqueous dispersion medium, and therefore ofthe indicator dispersion, and narrow the difference between the meltingpoint and the freezing point of the indicator dispersion.

Useful ice nucleants include inorganic ice nucleants and proteinaceousice nucleants derived from microorganisms. Some examples of usefulinorganic ice nucleants include silver iodide, cold-precipitated silveriodide/silver bromide mixtures and copper sulfide. An example of auseful proteinaceous ice nucleant is SNOMAX (trademark) snow inducer, afreeze-dried proteinaceous material available from Johnson ControlsInc., Milwaukee, Wis., www.johnsoncontrols.com. Some suitable icenucleants are also described in Taylor '980, for example, at paragraphs0322-0327.

Protein Stabilizer.

Freeze indicator embodiments that employ a proteinaceous ice nucleantcan include a protein stabilizer in the indicator dispersion tostabilize the ice nucleant against thermal or other degradation, ifdesired. Some examples of suitable protein stabilizers includeformaldehyde, glutaraldehyde (CHO.CH₂CH₂CH₂.CHO), and other dialdehydeshaving no more than ten carbon atoms. Some suitable protein stabilizersare also described in Taylor '980, for example, at paragraphs 0328 and0329.

Biocide.

A biocide can be included in the indicator dispersion of a freezeindicator embodiment that employs a proteinaceous ice nucleant, toprevent microbial spoilage, if desired. Certain protein stabilizers, forexample, glutaraldehyde and other dialdehydes, can also serve asbiocides, when used in an effective stabilizer concentration. Otherbiocides that can be employed, will be known, or apparent, to a personof ordinary skill in the art, in light of this disclosure.

Dispersion Stabilizer.

To help maintain the stability of the indicator dispersion, freezeindicator embodiments, can include a dispersion stabilizer. Optionally,the freeze indicator also can include a destabilizer to facilitatelow-temperature destabilization of the indicator dispersion, if adispersion stabilizer is present.

Some examples of suitable dispersion stabilizer include, surfactants,anionic surfactants, cationic surfactants, phosphate surfactants,zwitterionic surfactants, non-ionic surfactants, or a mixture of one ormore surfactants of similar type. As used herein, the term “non-ionicsurfactant” includes surfactants that are sometimes referenced in theart as “nonpolar.”

Some examples of particular surfactants that can be employed asdispersion stabilizers in freeze indicator embodiments include sodiumstearate, sodium dodecyl sulfate, dioctyl sulfosuccinate, ammoniumlauryl sulfate, lecithins, sodium dilauryl phosphate, betaine, laurylamido propyl dimethyl betaine, dodecyl trimethyl ammonium chloride,benzalkonium chloride, sorbitan monolaurate, and oleyl alcohol. Somefurther suitable dispersion stabilizers are also described in Taylor'980, for example, at paragraphs 0275-0301.

Any suitable amount of surfactant can be used to stabilize thedispersion, such as about 0.01% to about 10%, about 0.1% to about 5%,about 0.1% to about 1%, about 0.1% to about 0.5% or about 0.3% to about0.4% by weight, based upon the weight of the dispersion.

Low-Temperature Destabilizer.

Indicator dispersions employed in freeze indicator embodiments also caninclude a low-temperature destabilizer to promote or enhance coagulationof the freeze indicator dispersion at freezing temperatures, withoutunacceptably impairing the warm temperature stability properties of thedispersion, if desired.

The low-temperature destabilizer can be a concentration-sensitivedestabilizing or coagulating agent, for example, an ionic compound orcompounds, or another suitable compound or compounds such as a highmolecular weight compound. The destabilizing action of thelow-temperature destabilizer can depend upon the concentration of thedestabilizer in the aqueous liquid medium. Generally, although notnecessarily, a dispersion stabilizer also is present when alow-temperature destabilizer is employed.

Various materials can be employed as low-temperature destabilizersincluding various salts, such as inorganic salts, monovalent salts, andmultivalent salts. Some examples of suitable salts include thechlorides, sulfates, nitrates, and carboxylates of potassium, sodium,ammonium, calcium, and magnesium and mixtures of two or more of theforegoing salts.

Other materials that can be employed as low-temperature destabilizersinclude high molecular weight cationic, anionic, zwitterionic anduncharged polymers having a weight average molecular weight in the rangeof from about 1,000 Da to about 100,000 Da. Some examples of polymersuseful as low-temperature destabilizers in the practice of the inventioninclude polyacrylamides, polyvinyl alcohols, polyvinyl pyrrolidones, andpolyacrylic acids. Suitable polymers can be water-soluble and two ormore such polymers can be employed in a given indicator dispersion, ifdesired. Some suitable destabilizers are also described in Taylor '980,for example, at paragraphs 0302-0310 of Taylor '980.

The low-temperature destabilizer, if employed, can be selected forcompatibility with a particular dispersion stabilizer employed in agiven indicator dispersion. To illustrate, a polymeric destabilizeremployed with an ionically stabilized indicator dispersion can carry anopposite charge to the charge carried by the indicator dispersion. Forexample, a cationic polymer including quaternary ammonium segments canbe used to destabilize a stabilized indicator dispersion that employs ananionic stabilizer.

Proportions. A light-scattering freeze indicator dispersion employed ina freeze indicator embodiment can have any suitable proportions ofingredients compatible with providing a less colored before-freezingappearance and a more colored after-freezing appearance that hasadequate contrast to the before-freezing appearance to provide a goodfreeze exposure signal.

Where a hydrophobic liquid is employed, the indicator dispersion caninclude at least about 5 percent, at least about 20 percent, at leastabout 30 percent, or at least about 40 percent of the hydrophobic liquidby weight. Optionally, the indicator dispersion can include not morethan about 55 percent, not more than about 65 percent, or not more thanabout 75 percent of the hydrophobic liquid by weight. The range ofuseful variation of the proportion of hydrophobic liquid can lie betweenany one of the foregoing lower limits and any one of the foregoing upperlimits. All proportions described herein are by weight, based upon theweight of the indicator dispersion, unless the context indicatesotherwise. Other ingredients can be present in any suitable proportion.For example, the indicator dispersion can include a proportion by weightof an ice nucleant in a range of from about 0.01 percent to about 5percent or from about 0.2 percent to about 2 percent. Also, theindicator dispersion can include a proportion by weight of a dispersionstabilizer in a range of from about 0.1 percent to about 10 percent orfrom about 0.5 percent to about 5 percent. Further, the indicatordispersion can include a proportion by weight of a protein stabilizer offrom about 0.01 percent to about 1.0 percent or from about 0.05 percentto about 0.5 percent.

The aqueous liquid medium can make up the balance of the indicatordispersion. For example, depending upon the proportions of otheringredients present, the indicator dispersion can include from about 30percent to about 95 percent, or from about 40 percent to about 60percent of the aqueous liquid medium.

Some embodiments of freeze indicator consist exclusively of an aqueousliquid medium, colored indicator agent particles and, optionally, one ormore of a hydrophobic material, an ice nucleant, a protein stabilizer, adispersion stabilizer, a low-temperature destabilizer, and a biocide.Each of the ingredients can include more than one material, if desired.Other embodiments of freeze indicators can include an additionalingredient or ingredients.

With respect to indicator dispersions that are water-in-oil emulsions,in some embodiments, the aqueous phase can include a colorant with astrong affinity for the aqueous phase and low affinity for the oilphase. One suitable aqueous phase may include a dispersion of carbonblack in water, for example, a carbon black dispersion intended for ablack aqueous ink. The carbon black dispersion may be diluted withdistilled water to reduce the initial color intensity of the aqueousphase to reduce any excess color associated with the before freezingappearance of the indicator emulsion.

With respect to indicator dispersions that are water-in-oil emulsions,in some embodiments, the oil can be: a C₁₄ to C₁₈ aliphaticstraight-chain or branched saturated hydrocarbon, such as for example,hexadecane, isohexadecane, pentadecane, heptadecane, octadecane,tetradecane, etc., and mixtures thereof; an ester, including butylstearate, butyl myristate, tridecyl stearate, octastearate, isopropylmyristate, isocetyl myristate, isopropyl isostearate, etc. and mixturesthereof.

With respect to indicator dispersions that are water-in-oil emulsions,in some embodiments, an emulsifier and/or a surfactants could be used.Some examples of useful surfactants or emulsifiers include, but are notlimited to, hydrophobic nonionic surfactants, such as sorbitanmonooleate, polyoxyethylene sorbitan trioleate and sorbitan trioleate.

Some water-in-oil emulsions, such as water-in-oil emulsions that containonly non-ionic surfactants, may not coalesce sufficiently (or at all) tochange the appearance of the indicator following freezing conditionexposure. Such an emulsion can be deliberately destabilized, forexample, by adding a salt of a polynuclear, aromatic sulfonic acid, tothe mixture as a destabilizer. The sodium salt of xylene sulfonic acidis an example of a destabilizer. Other examples could includedodecylbenzylsulfonic acid (DDBSA), the sodium salt of xylene sulfonicacid (NAXSA), epoxylated and propoxylated compounds, anionic cationicand nonionic surfactants, resins such as phenolic and epoxide resins,etc.

Referring now to FIGS. 1 and 2 of the accompanying drawings, the freezeindicator shown, referenced 10, includes a substrate 12 supporting anenvelope 14 which contains a volume of an indicator dispersion 15 whichcan be any of the indicator dispersions described herein as being usefulin freeze indicator embodiments. As shown, envelope 14 can beapproximately circular. Alternatively, envelope 14 can have anotherdesired shape, for example, oval, hexagonal, square, rectangular,strip-like or ring-like. Envelope 14, as shown, includes an inner wall16 and an outer wall 18 joined together by a ring of adhesive 20, orjoined in another suitable manner, for example by fusing. Also, thejoint, or seal between inner wall 16 and outer wall 18 can have lowpermeability to water vapor. Alternatively, envelope 14 can be aone-piece sealed sac.

Inner wall 16 of envelope 14 can be adhered to, deposited on, orotherwise attached to, substrate 12 so as to attach envelope 14 tosubstrate 12. Alternatively, substrate 12 can provide inner wall 16 asan integral component of the substrate. For example, inner wall 16 caninclude a layer, or insert, of aluminum or other material substantiallyimpermeable to water vapor and aqueous liquids, formed integrally withsubstrate 12 or as a separate element.

Outer wall 18 of envelope 14 includes a transparent window (notreferenced) which can occupy approximately the entire footprint ofenvelope 14 on substrate 12, if desired. Alternatively, the transparentwindow can occupy a smaller area or the entire envelope 14 can betransparent. The transparent window enables an optical signal generatedby freeze indicator 10, for example, a change in color, to be readexternally by a suitable instrument, by a human viewer, by a camera, byan optical detector, or in another suitable manner. Envelope 14 can beformed of materials having a low permeability to water vapor to protectindicator dispersion 15 from drying out, if desired.

Optionally, outer wall 18 of envelope 14 can be provided with a colorfilter 22, for example, as a light-modulating coating of an ink, alacquer, a paint, or another suitable coating material on outer wall 18.Alternatively, color filter 22, can be a separate element such as aseparate layer. Color filter 22 can be transparent to enable theappearance of the indicator dispersion to be viewed through the filter.In one embodiment color filter 22 has a transparent green color,indicator dispersion 15 is light-colored before freezing, and isdark-colored or black after freezing, so that the freeze indicator showsa change from green before freezing to dark, or black, after freezing.

The freeze indicator illustrated in FIG. 3, referenced 24, can begenerally similar to that shown in FIGS. 1 and 2 with the differencesthat are apparent from the following description. Freeze indicator 24can include an upper blister and a lower substrate portion 26 definingbetween them an indicator volume 27 that can contain an indicatordispersion such as described herein. Upper blister portion 25 can bepreformed from a synthetic polymeric film material, for examplepolyvinyl chloride. Also, substrate portion 26 can be formed in onepiece with upper blister portion 25 and can be sealed to substrateportion 26 in any suitable manner, for example, by heat sealing or byuse of an adhesive. Alternatively, blister portion 25 and substrateportion 26 can be formed in one piece. Freeze indicator 24 can beflexible, if desired, for example sufficiently flexible that substrateportion 25 can conform to the curved surface of a desired host product.

Freeze indicator 24 can be embodied in a variety of configurations,including relatively small configurations. One illustrative example of asmall embodiment of freeze indicator 24 has a blister diameter (orequivalent dimension) of not more than about 4 mm, a blister height (thevertical dimension in FIG. 3) of not more than about 0.6 mm, and anindicator volume of not more than about 5 μL. Another example of alarger embodiment of freeze indicator 24 has a blister diameter (orequivalent dimension) of about 12 mm, a blister height (the verticaldimension in FIG. 3) of about 1.2 mm, and an indicator volume of about80 μL. These dimensions are merely exemplary and freeze indicator 24 canhave smaller or larger configurations.

Freeze indicator embodiments can have any suitable thickness in thedirection of optical reading, for example, in the case of the freezeindicator illustrated in FIGS. 1 and 2, a thickness up to about 1 mmbetween inner wall 16 and outer wall 18 across the envelope 14 in whichindicator dispersion 15 is accommodated. For some purposes, however,freeze indicator embodiments can have a thin or low profile, having athickness of the indicator dispersion of from about 10 μm (micron) toabout 0.3 mm, for example.

In some embodiments, the indicator dispersion may have a thickness ofless than about 1 mm, less than about 0.5 mm, less than about 0.2 mm, orless than about 0.1 mm.

Freeze indicator embodiments can have various other structuralcharacteristics including any of the structural characteristics of theinventive freeze indicators described in Taylor '980.

Some illustrative and nonlimiting examples follow of the preparation andcharacterization of indicator dispersions useful in the practice of theinvention.

Example 1: Preparation of a Light-Scattering Indicator Dispersion

In the following example, all parts are parts by weight based on theweight of the light-scattering indicator dispersion. To prepare alight-scattering indicator dispersion for a freeze indicator, 1 partSolvent Black BS (Orient Corp. of America, Seaford, Del.), which is anoil-soluble black dye, 5 parts of a nonionic surfactant (TERGITOL®15-S-15, Dow Chemical, Midland, Mich.) and 44 parts of a partiallyhydrogenated terphenyl oil (MCS 2811 Solutia, St. Louis, Miss.) areadded to a glass vial and heated to 80° C. using a water bath. A secondvial containing 50 parts of distilled water is also heated to 80° C. Ahomogenizer (IKA Ultra-Turrax T-18) is inserted into the hot dye-in-oilsolution and operated first at a low agitation speed setting until thetemperature reaches 80° C. The agitation rate is then increased to amoderate speed setting. The hot distilled water then is added slowly tothe hot dye-in-oil solution. After addition of 30 parts of the hotdistilled water, the mixture suddenly turns from black to dark gray andis opaque, indicating inversion of the emulsion. During the addition,the mixture suddenly turns from black to dark gray and opaque,indicating inversion of the emulsion. The remainder of the hot water inthe second vial is added, the heat is removed and the homogenizer isoperated at low speed until the mixture has returned to a temperaturenear to ambient (about 20° C. to about 25° C.).

Example 1 demonstrates that a light-scattering indicator dispersion canbe prepared by an inverse emulsion process to provide a product that isopaque and has a lighter appearance than the black oil phase of thedispersion. However, the difference between the before and afterappearances may be inadequate to provide a satisfactory freeze indicatorsignal.

Example 2

Example 1 is repeated to prepare Samples A-F using smaller proportionsof dye, as shown in Table 1.

TABLE 1 Composition of Option 1A Emulsion Formulations (parts) Sample AB C D E F Terphenyl Oil 44.25 44.88 44.94 44.99 44.995 44.998 Oil BlackBS 0.75 0.12 0.06 0.01 0.005 0.002 dye Surfactant 5.0 5.0 5.0 5.0 5.05.0 Distilled 50 50 50 50 50 50 Water Total 100 100 100 100 100 100

TABLE 1B Black intensity of Oil Black BS dye solution in terphenyl oilSample A B C D E F Oil alone Dye concentration in oil 1.69% 0.27% 0.13%0.02% 0.01% 0.004% 0 Oil Black BS dye solution 380* 60* 30* 4.5 2.2 0.80.0 in terphenyl oil absorbance at 500 nm *Absorbance by extrapolation

The visual blackness of the oil solutions of black dye was clearlyrelated to dye concentration. Direct measurement of absorbance at 500 nmwith 10 mm path length of each solution and oil alone, was attemptedusing a Shimadzu UV-2700 Spectrometer. Samples A, B, and C were toointense to measure directly. Samples D, E, F and dye-free oil gaveabsorbance vales within the reliable range of the instrument—they werealso linear with concentration and therefore able to be used tocalculate absorbance of the higher concentration samples A, B and C byextrapolation.

The before-freezing and after-freezing appearances of Samples A-F areshown in FIG. 4. Referring to FIG. 4, a before-freezing vial and anafter-freezing vial for each of the six Samples A-F is shown. The vialsare arranged side-by-side in a circle, with the vials for Sample A atthe top of the figure. The before-freezing vials are lighter in colorthan the corresponding after-freezing vials, which are adjacent thebefore-freezing vials in the clockwise direction. The weight proportionof dye-in-oil solution for each sample is shown next to the inward endsof each pair of vials. The vials are illuminated from the top left, asviewed in FIG. 4, so that the right hand side of some vials is partiallyshaded, darkening the appearance of that side of the vial. In each case,the indicator dispersion has a homogenous, opaque before-freezingappearance and the white samples, Samples B-F, have a creamy appearance.Also, the after-freezing appearance of the indicator dispersion of eachsample is substantially darker than the before-freezing appearance,consistently with the indicator dispersion having coagulated to revealthe dark appearance of the black-dyed oil.

Sample A, employing 0.75 percent dye-in-oil solution by weight, has adark grey appearance before freezing and a black appearance afterfreezing. The average particle size of the oil droplets in Sample A isabout 1 μm.

Sample B, employing 0.12 percent dye-in-oil solution by weight, has amedium grey appearance before freezing and a black appearance afterfreezing. The average particle size of the oil droplets in Sample A isabout 1.6 μm.

Sample C, employing 0.06 percent dye-in-oil solution by weight, has alight grey appearance before freezing and a black appearance afterfreezing. The average particle size of the oil droplets in Sample C isabout 1.4 μm.

Sample D, employing 0.01 percent dye-in-oil solution by weight, has anoff-white appearance before freezing and a black appearance afterfreezing. The average particle size of the oil droplets in Sample A isabout 1.1 μm.

Sample E, employing 0.005 percent dye-in-oil solution by weight, has anopaque, off-white appearance before freezing and a black appearanceafter freezing. The average particle size of the oil droplets in SampleE is about 700 nm.

Sample F, employing 0.002 percent dye-in-oil solution by weight, has anopaque, bright, white appearance before freezing and a black appearanceafter freezing. The average particle size of the oil droplets in SampleF is about 700 nm.

Samples D, E and F provide a strong contrast between the before-freezingand after-freezing appearances. These samples exhibit a light, bright,opaque before-freezing appearance and an intense black post-freezingappearance, providing a striking color change that would make a goodindicator signal. Samples D, E and F appear to be suitable for use in afreeze indicator.

Example 2 and the results shown in FIG. 4 illustrate how a suitableconcentration of colorant, in this case, a black dye, can provide anappropriately light before-freezing appearance and an appropriately darkafter-freezing appearance can be determined by simple experimentation.The concentrations of Oil Black BS dye employed in Samples A, B, and Cprovide dark before-freezing appearances whereas the proportionsemployed in Samples D, E and F provide useful light before-freezingappearances and satisfactorily dark after-freezing appearances. Theactual color of the oil, as measured by absorbance, demonstrates thesame relationship. Oil solutions that have absorbance of 30 or moreproduce emulsions that appear dark before-freezing, while those withabsorbance of 4.5 and lower produce emulsions that appear to have usefullight-before freezing appearances and satisfactorily dark after-freezingappearances. Further, there is a substantial absorbance range fromSample D (4.5) to Sample F (0.8) providing acceptable appearances withinwhich a skilled person can work to provide the desired before-freezingand after-freezing appearances using a particular colorant. Theconcentration of dye required to provide good or optimal before-freezingand after-freezing appearances is likely to vary widely betweencolorants according to the intensity of the particular colorantemployed, although the absorbance is likely to remain in or near therange defined by these samples.

Example 3: Preparation of a Light-Scattering Indicator Emulsion

In the following examples, the term “parts” refers to parts by weightbased on the weight of the light-scattering indicator emulsion. Toprepare this example of light-scattering indicator emulsion for a freezeindicator, 49.65 parts of partially hydrogenated terphenyl oil (MCS 2811Solutia, St. Louis, Mo.) is added to a glass griffin beaker withmagnetic stir bar and heated with stirring to 105° C.−110° C. with astirring hot plate. To that is added 0.025 parts Nigrosine Black EEL(Orient Corp. of America, Seaford, Del.), an oil-soluble black dye,0.325 parts sodium dioctyl sulfosuccinate (Aerosol OT 100%, CytecIndustries, Inc., Woodland Park, N.J.) an ionic surfactant. Continuestirring 30 min, then vacuum filter hot through a 410 filter paper withBuchner funnel. This oil/dye/surfactant solution is transferred to aclean glass beaker, the temperature adjusted to 70° C. and a homogenizer(IKA Ultra-Turrax T-18) is inserted into the hot dye-in-oil solution andoperated at a low agitation speed (1). 50 parts of deuterium oxide(Cambridge Isotope Laboratories, Inc., Andover Mass.) is warmed to 70°C. in a separate beaker and added slowly to the beaker ofoil/dye/surfactant solution and the homogenizer rate increased to 4-5.During the addition, the mixture suddenly turns from black to opaquelight gray. The stirrer is removed from the beaker and the beaker withemulsion covered and set on the bench counter at ambient conditions (1-2hr). The above emulsion is further processed in a high-pressurehomogenizer (Nano DeBee, Bee International, South Easton, Mass.) at anoperating pressure of 5000 psi.

After the high-pressure homogenization the emulsion is characterized byvisual and instrumental analysis: Z-average particle diameter 410 nm andpolydispersity index 0.38; pH 7.1. The opacity of the emulsion asdetermined by use of a Pfund Cryptometer (BYK—Gardner USA, Columbia,Md.) with a 0.007 top plate yields the obscuring of the black/whiteboundary at a scale reading of 19 mm which corresponds to a filmthickness of 0.13 mm. The color is white, slight grey with opticaldensity 0.4. The optical density of the emulsion was determined byreading through the optically clear wall of a container filled with theemulsion with a densitometer (X-Rite 504, X-Rite, Inc., Grand Rapids,Mich.). The container with emulsion is placed in a freezer (−10° C. 15m) and appears dark grey when removed from the freezer. This containerwith emulsion when analyzed for optical density in the above manneryields an OD of 1.3. The arithmetic difference of the post-freezemixture minus the optical density before freezing is referred to as thechange in optical density or 40 D. In the above example the 40 D is 0.9.

The light scattering emulsion described above is observed to havecontinuing stability at 60 days with regards to particle size, pH,opacity, and visual appearance.

Example 4

The procedure of Example 3 is followed to make a light scatteringemulsion with stearyl ether polypropylene glycol (Lipocol-15, LipoChemicals, Paterson, N.J.) in place of the partially hydrogenatedterphenyl oil used in Example 3.

After the high-pressure homogenization the emulsion is characterized byvisual and instrumental analysis: Z-average particle diameter 500 nm andpolydispersity index 0.11; pH 7.7. The opacity of the emulsion asdetermined by use of a Pfund Cryptometer (BYK—Gardner USA, Columbia,Md.) with a 0.007 top plate yields the obscuring of the black/whiteboundary at a scale reading of 44 mm which corresponds to a filmthickness of 0.32 mm. The color is light grey with optical density 0.6.After freezing the optical density is 1.6; providing a 40 D of 1.0.

Example 5

The procedure of Example 3 is followed in its entirety and additionalcomponents added as described herein: 99.5 parts of the emulsionprocessed by high-pressure homogenization is combined with 0.25 parts ofSnomax Snow Inducer (Johnson Controls Snow, Centennial, Colo.) and themixture is stirred 1 min followed by addition of 0.25 partsgluteraldehyde solution (Grade I, 50%, Sigma-Aldrich Corp., St. Louis,Mo.) and continue stirring for 1 min.

The freezing point of the emulsion is determined by direct, visualobservation of 25 replicate emulsion samples in 0.2 mL polypropylene PCRtubes with cap (Fisherbrand, Thermo Fisher Scientific, Inc., Waltham,Mass.) in a temperature controlled fluid bath (Fluke Calibration,Everett, Wash.). The tubes are mounted in a submersible rack devicedesigned to accommodate 25 PCR tubes. Each tube is charged with ameasured amount of freeze indicating emulsion and sealed with the cap.The rack with samples is submerged in the bath media and the temperatureis lowered in 0.1° C. increments beginning at 1.0° C. and continueduntil all samples have frozen. Emulsion sample freezing is observable bythe change in the emulsion from opaque white to black as seen throughthe transparent PCR tube. The results of freezing point determinationover a range of sample volumes are summarized in Table 2.

TABLE 2 Effect of Sample Volume on Freeze Onset and Appearance SampleVol. Mean Freeze Onset Appearance (μL) (° C.) Std. Deviation(initial/frozen) 80 −0.1 0.1 Slight gray/black 20 −0.3 0.1 Slightgray/black 10 −0.5 0.1 Slight gray/black 5 −0.3 0.2 Slight gray/black

Freeze indicator embodiments can be used with a variety offreeze-sensitive host products to indicate historically possibleexposure of the host product to a freezing temperature. Suitable hostproducts include any freeze-sensitive commercial product, for example,freeze-sensitive health care products, vaccines, drugs, medicaments,pharmaceuticals, biological pharmaceuticals, freeze-sensitivefoodstuffs, or freeze-sensitive industrial products. Some otherfreeze-sensitive host products that can be monitored by freeze indicatorembodiments are described in the Taylor et al. patent publications citedherein or will be known or apparent to a person of ordinary skill in theart, in light of this disclosure, or will become known or apparent inthe future.

Example 6

TABLE 3 Component Description Parts 1 n-Hexadecane 64 2 Sorbitanmonooleate 8 3 Polyoxyethylene sorbitan monooleate 5.6 4 Sorbitantrioleate 2.4 5 Highly colored aqueous dispersion 20

A water-in-oil emulsion for use as an indicator dispersion can be madeas follows using the components listed in Table 3. The emulsifier andsurfactants (sorbitan monooleate, polyoxyethylene sorbitan monooleate,and sorbitan trioleate) are added to the oil phase and mixed forapproximately 2-3 minutes with a homogenizer running at high speed. Ifsolubilization is incomplete, the mixture can be heated to about 60 to80° C. with a hot plate. The aqueous phase is added slowly to the oilphase (hot or cold) with continued mixing with the homogenizer. Mixingis continued for a short period after all the aqueous mixture has beenadded. If hot, the emulsion is permitted to cool with slow stirring.

This formula described above is for an indicator intended to respond attemperatures below about 18° C., the freezing point of hexadecane. For aconventional freeze indicator, the oil phase could be made from dodecaneethyl ester, with a freezing temperature of about −2° C., for example.

The desired result will be a system in which a strongly colored aqueousphase is incorporated in water-in-oil emulsion whereby the emulsion hassignificantly less color before exposure to temperatures below thefreezing point of either the oil or the aqueous phase. Exposure todecreasing temperatures will cause such emulsions to “break” oncefreezing occurs, resulting in a permanent, visually apparent change inappearance that can be utilized in the development of an indicator.

Some embodiments include a freeze-sensitive host product having a freezeindicator embodiment associated with it.

DISCLOSURES INCORPORATED

The entire disclosure of each United States patent, each United Statespatent application, each international patent publication, each foreignpatent publication, any other publication, and of each unpublishedpatent application identified in this specification is incorporated byreference herein, in its entirety, for all purposes. Should a conflictappear to be present between the meaning of a term employed in thedescription of the invention in this specification and the usage of theterm in material incorporated by reference from another document, themeaning of the term as used herein is intended to prevail. Any referenceto an “invention” in any incorporated disclosure is to be understood torefer to the invention described, or claimed, in the incorporateddisclosure.

ABOUT THIS DESCRIPTION

The detailed description herein is to be read in light of and incombination with the descriptions of the background to the invention andof the brief summary of the invention where information regarding thewritten description of the invention, the best mode of practicing theinvention, or description of modifications, alternatives or other usefulembodiments may also be set forth explicitly, or implied, as will beapparent to one skilled in the art.

The terms “include,” “have,” “has,” and “contain,” and their variousgrammatical forms, are to be understood as being open-ended and not toexclude additional, unrecited elements or method steps.

Throughout the description, where compositions instruments, devicesapparatus, systems, or processes are described as having, including, orcomprising specific components or elements, or in the case of processes,specific steps, it is contemplated that compositions instruments,devices apparatus, systems, or processes according to the presentinvention can also consist essentially of, or consist of, the recitedcomponents, elements or steps.

In this application, where an element or component is said to beincluded in and/or selected from a list or group of recited elements orcomponents, it should be understood that the element or component can beany one of the recited elements or components, or can be selected from agroup consisting of two or more of the recited elements or components.

The use of the singular herein is intended to include the plural (andvice versa) unless the context indicates otherwise.

Also, where the term “about”, “approximate”, “approximately”, or asimilar term, is used before a quantitative value, the specificquantitative value itself is to be understood to be included, and to beexplicitly recited, unless the description specifically statesotherwise.

With regard to processes, it is to be understood that the order of stepsor order for performing certain actions is immaterial so long as thedescribed process remains operable. Moreover, two or more steps oractions may be conducted simultaneously, unless the context indicatesotherwise. In addition, any proportions recited herein are to beunderstood to be proportions by weight, based upon the weight of therelevant composition, unless the context indicates otherwise. Also,unless the context indicates otherwise, or suggests otherwise, anymethods that are described herein, or one or more steps of the methods,can be practiced at a room temperature in the range of about 20° C. toabout 25° C.

The description of the background of the invention herein may includeinsights, discoveries, understandings or disclosures, or associationstogether of disclosures, that were not known in the relevant art priorto the present invention but which are provided by the invention, andare to be considered elements of the invention. Some such contributionsof the invention may have been specifically pointed out as beingattributable to the invention, and other such contributions of theinvention will be apparent from their context. Merely because a documentmay have been cited in this application, no admission is made that thefield of the document, which may be quite different from that of theinvention, is analogous to the field or fields of the present invention.

The description of the invention herein is to be understood as includingcombinations of the various elements of the invention, and of theirdisclosed or suggested alternatives, including alternatives disclosed,implied or suggested in any one or more of the various methods,products, compositions, systems, apparatus, instruments, aspects,embodiments, examples described in the specification or drawings, ifany, and to include any other written or illustrated combination orgrouping of elements of the invention or of the possible practice of theinvention, except for groups or combinations of elements that areincompatible with, or contrary to the purposes of the invention, as willbe, or will become, apparent to a person of ordinary skill. Further,embodiments can have any configuration that is described herein, or isshown in any accompanying drawings, and can employ any compatible onesof the useful materials or structures described herein.

SCOPE OF THE INVENTION

The present invention includes the examples and embodiments describedherein and other specific forms of the invention that embody the spiritor essential characteristics of the invention or of the respectivedescribed examples or embodiments. The foregoing examples andembodiments are in all respects intended to be illustrative of theinvention described herein. It is to be understood that many and variousmodifications of the invention, or of an example or embodiment describedherein will be apparent to those of ordinary skill in the relevant art,or may become apparent as the art develops, in the light of theforegoing description. Such modifications are contemplated as beingwithin the spirit and scope of the invention or inventions disclosedherein.

The invention claimed is:
 1. An indicator dispersion comprising: a liquid medium; and liquid particles of a colored indicator agent dispersed in the liquid medium, the colored indicator agent particles having an inherent color; wherein the indicator dispersion exhibits the inherent color of the colored indicator agent particles after freezing and is configured to have a less colored appearance before freezing and wherein light scattering masks the inherent color of the colored indicator agent particles before freezing.
 2. The indicator dispersion of claim 1, wherein the liquid medium is a hydrophobic liquid medium.
 3. The indicator dispersion of claim 1, wherein the liquid medium is an aqueous liquid medium.
 4. The indicator dispersion of claim 3, wherein the liquid particles of the colored indicator agent comprise a colorant dissolved or dispersed in a hydrophobic liquid.
 5. The indicator dispersion of claim 4, wherein the colorant is a dye and the hydrophobic liquid is an oil.
 6. The indicator dispersion of claim 4, wherein the liquid medium comprises D₂O.
 7. The indicator dispersion of claim 4, wherein the liquid medium comprises a mixture of D₂O and H₂O.
 8. The indicator dispersion of claim 1, wherein the liquid particles of the colored indicator agent comprise solid particles of a colorant dissolved or dispersed in a second liquid medium prior to freezing.
 9. The indicator dispersion of claim 1, wherein the indicator dispersion comprises a proportion by weight of colorant, based upon the weight of the indicator dispersion, of at least about 0.0005 percent and not more than about 1.0 percent by weight.
 10. The indicator dispersion of claim 1, wherein the particles of the colored indicator agent have an absorbance at 500 nm of about 1 to about
 30. 11. The indicator dispersion of claim 1, wherein the after-freezing appearance of a layer of the indicator dispersion having a thickness of 1 mm is at least 0.4 optical density units darker than the before-freezing appearance of the layer of the indicator dispersion.
 12. The indicator dispersion of claim 1, wherein the indicator dispersion comprises an ice-nucleating agent.
 13. The indicator dispersion of claim 1, wherein the mass ratio of the indicator dispersion to the total indicator dispersion is about 0.005:100 to about 0.6:100.
 14. The indicator dispersion of claim 1, wherein the particles of the colored indicator agent have an absorbance at 500 nm of about 1 to about
 30. 15. The indicator dispersion of claim 1, wherein the after-freezing appearance of a layer of the indicator dispersion having a thickness of 1 mm is at least 0.6 optical density units darker than the before-freezing appearance of the layer of the indicator dispersion.
 16. The indicator dispersion of claim 1, wherein the after-freezing appearance of a layer of the indicator dispersion having a thickness of 1 mm is at least 0.9 optical density units darker than the before-freezing appearance of the layer of the indicator dispersion.
 17. The indicator dispersion of claim 1, wherein the indicator dispersion further comprises a dispersion stabilizer.
 18. The indicator dispersion of claim 1, wherein the indicator dispersion further comprises a low-temperature destabilizer.
 19. The indicator dispersion of claim 1, wherein the indicator dispersion further comprises an additive, the inclusion of which achieves a freezing temperature for the indicator dispersion that is less than 0° C.
 20. The indicator dispersion of claim 1, wherein the indicator dispersion further comprises an additive, the inclusion of which achieves a freezing temperature for the indicator dispersion that is greater than 0° C.
 21. An article of manufacture comprising a freeze indicator, the freeze indicator further comprising: a housing; and the indicator dispersion of claim 1 within the housing, the housing being configured for the indicator dispersion to be optically readable externally of the freeze indicator.
 22. The article of manufacture of claim 21, further comprising a substrate supporting the housing.
 23. The article of manufacture of claim 22, wherein the housing and substrate are flexible.
 24. The article of claim 21, further comprising a label for a perishable good containing the freeze indicator.
 25. The article of claim 21, further comprising a package for a perishable good, the freeze indicator being located on or in the package.
 26. The article of claim 25, further comprising the perishable good contained in the package.
 27. The article of claim 26, wherein the perishable good is a vaccine.
 28. The article of manufacture of claim 21, wherein the volume of the indicator dispersion within the housing is about 5 μL.
 29. A method of making a freeze indicator comprising: dispersing particles of a colored indicator agent in an aqueous liquid medium to provide an indicator dispersion; and loading the indicator dispersion into a housing permitting the indicator dispersion to be optically readable externally of the freeze indicator; wherein the colored indicator agent particles imbue the indicator dispersion with a more colored appearance after freezing; and wherein the indicator dispersion is configured to have less color before freezing.
 30. A method according to claim 29, wherein the colored indicator agent particles have an average particle size of at least about 100 nm and not more than about 2 μm.
 31. A method according to claim 29, wherein the indicator dispersion includes no color-changing chemical co-reactants.
 32. A method according to claim 29, wherein the indicator dispersion is configured to coagulate in response to exposure of the indicator dispersion to a freezing temperature.
 33. A method according to claim 29, wherein the indicator dispersion is configured to coalesce in response to exposure of the indicator dispersion to a freezing temperature.
 34. The method according to claim 29, wherein dispersing particles of a colored indicator agent in an aqueous liquid medium comprises: mixing together the colored indicator agent and a hydrophobic liquid to produce a hydrophobic mixture; and mixing together the hydrophobic mixture and the aqueous liquid medium to produce the indicator dispersion.
 35. The method of claim 34, wherein the aqueous liquid medium comprises D₂O.
 36. The method of claim 34, wherein the aqueous liquid medium comprises a mixture of H₂O and D₂O.
 37. The method of claim 34, wherein mixing together the hydrophobic mixture and the aqueous liquid medium further comprises adding at least one of an ice-nucleating agent, a protein stabilizer, a biocide, a dispersion stabilizer, and a low-temperature destabilizer.
 38. The method of claim 34, wherein mixing together the hydrophobic mixture and the aqueous liquid medium comprises homogenization.
 39. The method of claim 38, wherein the homogenization is performed at a high pressure.
 40. The method of claim 39, wherein the pressure is about 5000 psi.
 41. The method of claim 39, wherein the high pressure homogenization is performed until the particles of the colored indicator agent have an average size of about 100 nm to about 400 nm.
 42. The method of claim 34, wherein a surfactant is used to help mix the colored indicator agent and the hydrophobic liquid.
 43. The method of claim 42, wherein the surfactant comprises about 0.01 to about 1 wt % of the hydrophobic mixture.
 44. The method of claim 42, wherein the surfactant comprises about 0.1 to about 0.5 wt % of the hydrophobic mixture. 